The present invention relates to the specific field of turbomachines, and more particularly it relates to the problem posed by mounting a combustion chamber made of ceramic matrix composite (CMC) type material in the metal chamber casings of a turbomachine.
Conventionally, in a turbojet or a turboprop, the high pressure turbine (HPT) and in particular its inlet nozzle, the combustion chamber, and the inner and outer shells (or casings) of said chamber are all made of the same material, generally a metal. Nevertheless, under certain particular conditions of use, implementing very high combustion temperatures, using a metal combustion chamber turns out to be entirely inappropriate from a thermal point of view and it is necessary to use a chamber based on high temperature composite materials of the CMC type. However, the difficulties of working such materials and their raw materials costs mean that their use is generally restricted to the combustion chamber itself, with the inlet nozzle of the high pressure turbine and the inner and outer shells containing the chamber then continuing to be made more conventionally out of metal materials. Unfortunately, metal materials and composite materials have coefficients of thermal expansion that are very different. This gives rise to particularly severe problems of connection with the inner and outer shells and at the interface with the inlet nozzle to the high pressure turbine.
The present invention mitigates those drawbacks by proposing a mount for the combustion chamber within the casings, which mount has the ability to absorb the displacements induced by the different expansion coefficients of these parts. Another object of the invention is to propose a mount which makes best use of the existing characteristics of the combustion chamber.
These objects are achieved by a turbomachine comprising inner and outer annular shells of metal material containing, in a gas flow direction F: a fuel injection assembly; an annular combustion chamber of composite material having a longitudinal axis and a plurality of oxidizer feed orifices; and an annular nozzle of metal material having fixed blades and forming the inlet stage of a high pressure turbine, wherein said combustion chamber of composite material is held in position between said inner and outer annular metal shells by a plurality of flexible metal tongues, first ends of said tongues being interconnected by respective metal rings fixed securely to each of said inner and outer annular metal shells by first fixing means, and second ends of said tongues being fixed securely to said composite material combustion chamber via at least a fraction of said oxidizer feed orifices by second fixing means, the flexibility of said fixing tongues serving, at high temperatures, to accommodate free displacement in radial and axial directions between said composite material combustion chamber and said inner and outer annular metal shells. The oxidizer feed orifices are constituted by holes for feeding air to a primary zone and/or a dilution zone of said combustion chamber.
With this particular fixed connection structure, the various kinds of wear due to contact corrosion in prior art systems can be avoided. Using the primary holes or the dilution holes (depending on the intended chamber configuration) as anchor points also serves to simplify the connection considerably and to reduce the size thereof. In addition, the presence of flexible tongues taking the place of traditional flanges makes it possible to achieve an appreciable weight saving. Because of their flexibility, these tongues make it easy to accommodate the expansion difference that appears at high temperatures between metal parts and composite parts (by accommodating the displacements due to expansion) while continuing to hold the combustion chamber and keep it properly centered within the annular shells.
The flexible fixing tongues are made of a metal material and the first fixing means are preferably constituted by a plurality of bolts.
In one possible embodiment, said first ends of the tongues are connected by brazing or welding to said rings or else they are formed integrally therewith. When said annular metal shell is made up of two portions, each ring is preferably mounted between connecting flanges between said two portions of said annular metal shell.
In a preferred embodiment, each of said second fixing means comprising a collar inserted in the oxidizer feed orifice of said combustion chamber and is crimped to the second ends of the tongues so as to ensure that said tongues are held against the combustion chamber once the crimping has been achieved.
In an alternative embodiment, said second fixing means comprise a plurality of inserts each comprising two coaxial parts that are fixed one on the other, comprising firstly a collar pressed against a side wall of the combustion chamber and secondly a ring surrounding said collar and pressing the second ends of the tongues against said side wall.
Advantageously, said tongues have respective openings formed close to their second ends in order to improve the feed of oxidizer to said feed orifices.
The stream of gas is preferably sealed between said combustion chamber and said nozzle by a circular xe2x80x9cspring-bladexe2x80x9d type gasket bearing directly against a downstream end of said combustion chamber which forms a bearing plane for said circular gasket.